1. Field of the Invention
The present invention relates to an improvement of a drive force sharing control of a hybrid powered vehicle, which utilizes motive power of an internal combustion engine in combination with power of an electric motor. In particular, the present invention relates to an improvement of a sharing control of load shares of an internal combustion engine and an electric motor of a hybrid powered vehicle for a required drive force of the vehicle by controlling a ratio of a load sharing of the electric motor to that of the internal combustion engine according to a pressing amount of an accelerator pedal of the vehicle to economize fuel consumption of the hybrid powered vehicle.
2. Description of Related Art
When a running state of a usual hybrid powered vehicle, which includes an internal combustion engine and an electric motor, is in a start mode, an acceleration mode or a hill clamming mode, in which a larger drive force, the hybrid powered vehicle is usually set to an auxiliary acceleration mode to use the electric motor to generate a drive force to be added to a drive force of the internal combustion engine. In such case, the internal combustion engine, which utilizes liquid fuel, and the electric motor, which utilizes electric power, generate drive forces respectively correspondingly to a pressing amount of an accelerator pedal of the hybrid powered vehicle operated by a driver to share loads necessary to achieve the running mode.
In such conventional hybrid powered vehicle, an output signal of an acceleration sensor of the hybrid powered vehicle corresponding to the pressing amount of the accelerator pedal is usually supplied to both an internal combustion engine control circuit for controlling a flow rate of fuel to be supplied to the internal combustion engine and a hybrid control circuit for controlling an electric current to be supplied to the electric motor, in parallel. The internal combustion engine control circuit and the hybrid control circuit generate control outputs, according to respective control logics thereof. The pressing amount of the accelerator pedal operated by the driver corresponds to a mere comprehensive output power of the internal combustion engine and the electric motor. The driver may further press the accelerator pedal if he wishes to accelerate the vehicle further or release the accelerator pedal if he wishes to decelerate the vehicle. Therefore, in the conventional hybrid powered vehicle, the control circuit for the internal combustion engine and the control circuit for the electric motor of the conventional hybrid powered vehicle are constructed such that each of these control circuits controls the acceleration and the deceleration of the vehicle independently of the other.
Consequently, although the comprehensive drive force outputted by the internal combustion engine and the electric motor corresponds to the pressing amount of the accelerator pedal at a time when the accelerator pedal is operated by the driver, load required at that time and shared by the internal combustion engine and the electric motor are not determined constantly. That is, for example, the power control responsive to an operation input corresponding to the pressing amount of accelerator pedal includes a hysteresis and the hysteresis characteristics of the internal combustion engine is different from that of the electric motor. Therefore, even if the accelerator pedal is being pressed to a certain specific amount, the load sharing rates of the internal combustion engine and the electric motor are varied upon a changing history of the depression amount of the accelerator pedal before the certain specific pressing amount of the accelerator pedal is achieved.
The above mentioned fact that the load sharing rates of the internal combustion engine and the electric motor are not determined constantly with respect to the constant pressing amount of the accelerator pedal is caused by not only the hysteresis characteristics of the internal combustion engine control circuit and the hybrid control circuit but also various other phenomena. For example, the other phenomena may include a temperature of the internal combustion engine, a charging rate of a storage battery for supplying current to the electric motor and a pressing speed of the accelerator pedal. As such, in the conventional control device, the load sharing rates of the internal combustion engine and the electric motor with respect to the pressing amount of the accelerator pedal are always varied according to changes of such various factors as mentioned above.
Response characteristics of an internal combustion engine and an electric motor to the pressing amount of the accelerator pedal are disclosed in JP H10-23608A and JP H08-294205A.
It has been found by the inventors of the present invention that, if the load sharing rates of the internal combustion engine and the electric motor with respect to the pressing amount of the accelerator pedal is not determined constantly, it may be impossible to make the performance of the hybrid powered vehicle best. That is, the most important feature of the hybrid powered vehicle is to ensure that the fuel consumption per unit running distance is as small as possible. In order to use this feature practically, it is necessary to maintain the charging rate of the storage battery as high as possible by charging the storage battery by means of regenerative braking during deceleration and to increase the rate of auxiliary motor running during acceleration. In order to increase the rate of auxiliary motor running during acceleration, it is necessary to execute a control for increasing the rate of auxiliary motor running as much as possible.
As a result of detailed investigation of this matter of a hybrid powered vehicle having conventional design conducted by the inventors, it has been found that, in a region in which the pressing amount of the accelerator pedal is one third of the full pressing or smaller, that is, a comprehensive output torque of the vehicle is small, the load sharing rates of the internal combustion engine and the electric motor are varied considerably due to various influences. Therefore, even if the hybrid powered vehicle is designed in such a way that efficiencies of the internal combustion engine and the electric motor become optimal with respect to drive forces generated thereby, the load sharing of the internal combustion engine is increased and the comprehensive fuel efficiency of the hybrid powered vehicle is degraded when the load sharing rates become inadequate.